Idiopathic Normal Pressure Hydrocephalus (INPH) is an important cause of dementia, gait disturbance, and incontinence in the elderly. It may be confused with Alzheimer's Disease (AD); unlike AD, however, it may be markedly improved by cerebrospinal fluid (CSF) shunting. Because CSF shunting may have substantial morbidity, it is important to select patients carefully. There are presently no reliable criteria for deciding to shunt. This proposal has two goals: to clarify the diagnostic differences between INPH and AD, and to evaluate three tests presently thought to predict a good shunt response in INPH. The study will test three measures presently thought to distinguish INPH from AD: concentrations of the peptides vasopressin and somatostatin in CSF, atrophy and periventricular lucency on computed tomographic and magnetic resonance imaging, and gait and psychometric test profile. These features will be compared in 50 patients given the diagnosis of INPH over a three year period with 50 others given the diagnosis of AD. To help establish predictive tests for INPH, the study will use the tests just described as well as overnight recording of CSF pressure, lumbo-ventricular perfusion of CSF, and withdrawal of 50 cc of CSF with subsequent analysis of gait. Domain analysis as well as analysis of variance will be used in the statistical evaluation of these measures. This study will provide the first prospective and rigorous testing of several criteria thought to distinguish INPH from AD and predict a good shunt response. By refining criteria for diagnosis and shunt placement it will be a major contribution to the management of gait and memory disorder in the elderly.